An Interpretation Of The Retention Of Low Energy Deuterium Ions In Tungsten

Abstract

This report is a summary of our investigations of D retention in various forms of tungsten: high purity polycrystalline W (PCW), polycrystalline W containing 1% La₂O₃, and two grades of single crystal W (SCW). The experiments have been primarily implantations followed by thermal desorption measurements. Nuclear reaction analysis and SIMS were used to measure the depth distributions near the surface. By using low energy ions (500 eV/D⁺), it has been possible to eliminate most if not all elastic collision defect creation, yet this has not reduced the trapping significantly. Comparing the results for the various forms of W has enabled us to assess the effects of grain boundaries, dislocations and impurities. Recent work has included a study of the effects of ion flux on deuterium retention in SCW. The conclusion drawn is that D is trapped in clusters or nano-bubbles, and that these traps grow with increasing fluence, particularly at higher temperatures. The large variations in the retention of D in W show that the processes controlling D trapping are many and complex. In order to form a more comprehensive picture, and eventually attempt to predict retention under fusion relevant conditions, modeling has been performed using TMAP4[1].